1. Field of the Invention
The present invention relates to an electronic ballast for an fluorescent lamp (CF lamp), and more particularly, to an electronic ballast for an fluorescent lamp capable of turning on lamps of different capacitances (36W, 18W, etc.), or selectively turning on two lamps of the same capacitance or one lamp, using one circuit, by replacing a conventional lamp driving circuit with an integrated circuit (IC).
2. Background of the Related Art
In general, lighting fixtures that emit light such as an incandescent light, a fluorescent lamp, and the like are attached to given locations (in particular, ceiling) in an office, homes, buildings, and the like, in order to make light surrounding environments when it gets dark. Those lighting fixtures are replaced with new ones after their power are run out.
The fluorescent lamp of these lighting fixtures might be classified largely into a transformer mode and a ballast mode.
A compact fluorescent lamp (CFL) that has been widely used has a ballast element and a screw element on the top of the lamp. It can be thus easily used as a socket for a common incandescent light.
The lamp socket of a socket type for use in the incandescent light, the fluorescent lamp, etc. has been widely used for interior illumination in common homes, offices, etc. or inner illumination within refrigerators, microwave ovens, etc.
FIG. 1 is a circuit diagram of conventional electronic ballast for 220V.
As shown in FIG. 1, the electronic ballast includes the power supply 101; a power supply unit 110 having a fuse F that is short-circuited in order to prevent in advance damage of the circuit due to a high voltage when the voltage of the power supply 101 exceeds a predetermined voltage, a varistor B1 connected between both supply ends of the power supply 101 for stabilizing the AC power, a filter 111 for removing noise from the power, and a plurality of condensers C2˜C4 for voltage stabilization; a direct-current (DC) transformation unit 200 having a bridge diode BD, an inductance L2 and a smoothing condenser C5, for rectifying the AC (alternating current) power (220V) supplied from the power supply unit 110 into a DC power; and a lamp driving unit 300 that oscillates according to the power supplied from the DC transformation unit 200 to turn on the lamp.
In the above, the lamp driving unit 300 includes power transistors Q1 and Q2 connected to the bridge diode BD and the smoothing condenser C5 of the DC transformation unit 200, for performing a switching operation in order to generate an oscillation voltage for turning on the fluorescent lamp, oscillation coils L1, L2 and L3 connected to the power transistors Q1 and Q2, for generating a frequency of 25 Khz˜30 Khz depending on the values of the coils, a bulb BULB connected to the oscillation coils L1, L2 and L3, for turning on the fluorescent lamp using a voltage of a high frequency, diodes D10 and D11 and condensers C10 and C11, which are connected between the oscillation coil L3 and the bulb BULB, for offsetting a surge voltage generating when the lamp is connected to the socket in order to protect the lamp and the socket, a plurality of diodes D5˜D9 for protecting the power transistors Q1 and Q2, and a triac TA1 for preventing line surge applied to the base of the power transistor Q2.
One exemplary operation of the fluorescent lamp for the electronic ballast constructed above will be below described.
AC 220V of the power supply 101 is inputted to the power supply unit 110. In the power supply unit 110, the filter 111 filters the AC power through the fuse F to remove line noise from it. Next, the plurality of the condensers C2˜C4 stabilize the AC power and then transmit the resulting AC power to the DC transformation unit 200.
In the DC transformation unit 200, the bridge diode BD full-wave rectifies the inputted AC power. Next, the smoothing condenser C5 makes smooth the AC power and then converts it into a DC power. Thereafter, the DC power is transferred to the lamp driving unit 300 through the inductance L2.
In the lamp driving unit 300, the power transistors Q1 and Q2 are repeatedly turned on and turned off according to the DC power. Accordingly, high-frequency oscillation occurs through the oscillation coils L1, L2 and L3, which then turns on the lamp.
In other words, the voltage that was rectified as the DC power in the DC transformation unit 200 is applied to the power transistors Q1 and Q2 via the resistor R11, the diode D5, the condenser C7 and the triac TA1. Also, the power transistors Q1 and Q2 are alternately operated according to the DC power.
In particular, the power transistors Q1 and Q2 oscillate in a frequency of 25 Khz˜30 Khz depending on the values of the oscillation coils L1, L2 and L3 connected to the bases of the power transistors Q1 and Q2. This oscillation voltage results in supplying an instantly high voltage through the CT coil and the condenser C9 of the bulb BULB, to both ends of the lamp. Therefore, the lamp is turned on while a gas within the lamp is ionized.
Further, the diodes D10 and D11 and the condensers C10 and C11, which are connected between the oscillation coil L3 and the bulb BULB, offset the surge voltage occurring when the lamp is connected to the socket, whereby flickering of the lamp is removed.
FIG. 2 is a circuit diagram of a conventional electronic ballast for 120V.
As shown in FIG. 2, the electronic ballast includes the power supply 601; a power supply unit 610 having a fuse F that is short-circuited in order to prevent in advance damage of the circuit due to a high voltage when the voltage of the power supply 601 exceeds a predetermined voltage, a varistor B1 connected between both supply ends of the power supply 601 for stabilizing an AC power, a filter 611 for removing noise from the power, and a plurality of condensers C1˜C3 for voltage stabilization; a DC transformation and boosting unit 700 having diodes D12 and D13 and condensers C13 and C14 for rectifying the AC power (120V) supplied from the power supply unit 610 to be a DC power and then boosting it twice; and a lamp driving unit 300 that oscillates according to the power supplied from the DC transformation and boosting unit 700 to turn on the lamp.
In the above, the lamp driving unit 300 includes power transistors Q1 and Q2 connected to the DC transformation and boosting unit 700, for performing a switching operation in order to generate an oscillation voltage for turning on the fluorescent lamp, oscillation coils L1, L2 and L3 connected to the power transistors Q1 and Q2, for generating a frequency of 25 Khz˜30 Khz depending on the values of the coils, a bulb BULB connected to the oscillation coils L1, L2 and L3, for using a voltage of a high frequency to turn on the fluorescent lamp, diodes D10 and D11 and condensers C10 and C11, which are connected between the oscillation coil L3 and the bulb BULB, for offsetting a surge voltage occurring when the lamp is connected to the socket in order to protect the lamp and the socket, a plurality of diodes D5˜D9 for protecting the power transistors Q1 and Q2, and a triac TA1 for preventing line surge applied to the base of the power transistor Q2.
Another exemplary operation of the fluorescent lamp for the electronic ballast constructed above will be below described.
AC 120V of the power supply 601 is inputted to the power supply unit 610. In the power supply unit 610, the filter 611 filters the AC power through the fuse F to remove line noise from the AC power. Next, the plurality of the condensers C1˜C3 stabilize the AC power and then transmit the stabilized AC power to the DC transformation and boosting unit 700.
In the DC transformation and boosting unit 700, the diodes D12 and D13 rectify the AC power to be a DC power. Next, the condensers C13 and C14 boost the DC power twice and then transfer it to the lamp driving unit 300.
In the lamp driving unit 300, the power transistors Q1 and Q2 are repeatedly turned on and turned off according to the DC power. Accordingly, high-frequency oscillation occurs through the oscillation coils L1, L2 and L3, which then turn on the lamp.
In other words, the DC power that was boosted to the DC power twice in the DC transformation and boosting unit 700 is transferred to the power transistors Q1 and Q2 via the resistor R11, the diode D5, the condenser C7 and the triac TA1. Also, the power transistors Q1 and Q2 are alternately operated according to the DC power.
In particular, the power transistors Q1 and Q2 oscillate in a frequency of 25 Khz˜30 Khz depending on the values of the oscillation coils L1, L2 and L3 connected to the bases of the power transistors Q1 and Q2. This oscillation voltage results in supplying an instantly high voltage through the coil CT and the condenser C9 of the bulb BULB, to both ends of the lamp. Therefore, the lamp is turned on while a gas within the lamp is ionized.
Further, the diodes D10 and D11 and the condensers C10 and C11, which are connected between the oscillation coil L3 and the bulb BULB, offset the surge voltage occurring when the lamp is connected to the socket, whereby flickering of the lamp is removed.
This conventional electronic ballast, however, employs the power supply of the circuit that oscillates at high frequency to drive the lamp and the lamp power supply for turning on the lamp, as single power supply. Due to this, the conventional electronic ballast has disadvantages that the power factor is low and the overall operation of the circuit is unstable due to interference, etc.
Further, the conventional electronic ballast circuit is implemented using an analog circuit in which the lamp driving unit has a fixed value. Due to this, there is a problem that only one lamp corresponding to a corresponding capacitance could be driven but a plurality of lamps having different capacitances could not be driven.
Also, as described above, the conventional electronic ballast circuit is implemented using the analog circuit having a fixed value. Due to this, there is a disadvantage that when lamps having different capacitances are to be turned on, the circuit has to be modified accordingly.